Future tyre certification standards are expected to call for a reduction in the maximum noise level produced as the tyre rolls along the road surface; which means steps must be taken forthwith to reduce such noise.
Patent Application WO2009053353A1 describes a low-noise tyre, in which the tread strip grooves contain fine (therefore highly flexible) threads of 20-80 micron in diameter, and made of material (nylon, PET, acrylic, cotton, linen, wool or rayon) other than the rubber from which the tread strip is made. The threads inside the grooves have a fairly high density (2-50 threads/mm2) and serve to prevent the formation inside the grooves of stationary pressure waves resulting in noise emissions in the audible range (roughly between 1 and 4 kHz).
The threads described in Patent Application WO2009053353A1, however, are extremely complicated (therefore, expensive) to produce, by having to attach to the tread rubber a large number of fine threads of material (normally plastic) different from that of the tread. Moreover, attachment of the threads to the tread rubber must be mechanically strong enough to withstand the stress produced, as the tyre rolls along the road surface, by the centrifugal force generated by rotation and deformation of the tread at the point contacting the road surface. As the tyre rolls, the threads in the tread strip grooves also tend to get entangled in uneven road surfaces and so ripped out from the tread strip.
Patent Application JP9002020 describes a low-noise tyre, in which the longitudinal grooves in the tread strip contain noise-reducing pins projecting from the lateral walls of the grooves to a maximum length of 0.5 to 3.0 mm.
Patent Application JP2006137231 describes a tyre, in which the lateral longitudinal grooves in the tread strip contain pins projecting from the lateral walls of the grooves to a maximum length of 0.5 to 3.0 mm.